U.S. patent application number 13/847171 was filed with the patent office on 2013-09-19 for method for operating a combined cycle power plant and plant to carry out such a method.
This patent application is currently assigned to ALSTOM Technologies Ltd. The applicant listed for this patent is ALSTOM TECHNOLOGIES LTD. Invention is credited to Andrea Brighenti, Karsten Franitza, Darrel Shayne Lilley, Anton Nemet.
Application Number | 20130239573 13/847171 |
Document ID | / |
Family ID | 47790109 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130239573 |
Kind Code |
A1 |
Brighenti; Andrea ; et
al. |
September 19, 2013 |
METHOD FOR OPERATING A COMBINED CYCLE POWER PLANT AND PLANT TO
CARRY OUT SUCH A METHOD
Abstract
Disclosed is a method for operating a gas turbine (11)
comprising a compressor (14), which is equipped with variable inlet
guide vanes (13) and receives at its inlet an inlet air flow, which
has passed a temperature-affecting air inlet system (12a), a
combustor (15, 15') and a turbine (16, 16'). In a closed loop
control scheme, a control variable indicative of the turbine outlet
temperature (TAT2) is generated, and the air inlet system (12a)
and/or the variable inlet guide vanes (13) are controlled in
accordance with said control variable such that the turbine outlet
temperature (TAT2) is kept at or above a desired setting value
(TAT2.sub.min).
Inventors: |
Brighenti; Andrea;
(Wettingen, CH) ; Lilley; Darrel Shayne;
(Remetschwil, CH) ; Franitza; Karsten; (Baden,
CH) ; Nemet; Anton; (Lengnau, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM TECHNOLOGIES LTD |
Baden |
|
CH |
|
|
Assignee: |
ALSTOM Technologies Ltd
Baden
CH
|
Family ID: |
47790109 |
Appl. No.: |
13/847171 |
Filed: |
March 19, 2013 |
Current U.S.
Class: |
60/643 |
Current CPC
Class: |
F01K 21/00 20130101;
F05D 2270/0831 20130101; F05D 2270/303 20130101; F05D 2270/083
20130101; Y02E 20/16 20130101; F02C 9/20 20130101; F02C 6/18
20130101; F01K 23/101 20130101; Y02E 20/14 20130101; F02C 3/30
20130101 |
Class at
Publication: |
60/643 |
International
Class: |
F01K 21/00 20060101
F01K021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2012 |
EP |
12160146.2 |
Claims
1. Method for operating a combined cycle power plant comprising, a
gas turbine (11) with an inlet temperature affecting air inlet
system (12a-c) for adjusting the temperature of inlet air, a
compressor (14) downstream of the inlet temperature affecting air
inlet system (12a-c), for increasing the pressure of the air, and
which is equipped with variable inlet guide vanes (13) for
adjusting the inlet mass flow, at least one combustor (15, 15')
downstream of the compressor for combustion of fuel with compressed
air from the compressor (14), and at least one turbine (16, 16')
downstream of the combustor (15, 15') for expanding hot combustion
gases thereby generating mechanical power; a HRSG (18) downstream
of the gas turbine (11) for generating live steam; a steam turbine
(19) for expanding the live steam thereby generating mechanical
power; and a control system (22), characterized in that, in a
closed loop control scheme, a control variable indicative of the
live steam temperature (T.sub.steam) is generated, and that the
inlet temperature affecting air inlet system (12a-c) and/or the
variable inlet guide vanes (13) are controlled in accordance with
said control variable such that the live steam temperature
(T.sub.steam) is kept at or above a desired target steam
temperature (T.sub.steam,t).
2. Method according to claim 1, characterized in that the live
steam temperature (T.sub.steam) is directly measured and the
measured temperature is used as the control variable.
3. Method according to claim 1, characterized in that the turbine
outlet temperature (TAT2) is used as variable indicative of the
live steam temperature (T.sub.steam), and in that the turbine
outlet temperature (TAT2) is used as the control variable.
4. Method according to claim 3, characterized in that the turbine
outlet temperature (TAT2) is directly measured.
5. Method according to claim 3, characterized in that the turbine
outlet temperature (TAT2) is calculated from an on-line heat
balance calculation.
6. Method according to claim 3, characterized in that emissions, at
the outlet of the gas turbine (11) are measured and used as the
control variable.
7. Method according to claim 1, characterized in that a temperature
is measured at other parts of the gas turbine (11), especially at
the last stage vanes of the turbine (16, 16'), and this measured
temperature is used as a control variable.
8. Method according to claim 1, characterized in that the inlet air
is heated in the inlet temperature affecting air inlet system (12a)
until the live steam temperature (T.sub.steam) is at or above the
target steam temperature (T.sub.steam,t).
9. Method according to claim 8, characterized in that compressed
air from a rear stage of the compressor is used to heat up the
inlet air in the inlet temperature affecting air inlet system
(12a).
10. Method according to claim 8, characterized in that part of flue
gases are recirculated and admixed to the inlet air in the inlet
temperature affecting air inlet system (12d) to heat up the inlet
air.
11. Method according to claim 1, characterized in that during part
load operation a cooling air mass flow of the gas turbine (11) is
reduced and/or a re-cooling temperature of a cooling air cooler is
increased to increase the live steam temperature (T.sub.steam).
12. Method according to claim 1, characterized in that the intake
air is cooled in the inlet temperature-affecting inlet system (12b)
to reduce the live steam temperature (T.sub.steam) to the target
steam temperature (T.sub.steam,t).
13. Method according to claim 1, characterized in that the output
power of the plant is controlled by controlling the position of the
variable inlet guide vanes (13) and the turbine inlet temperature,
and in that the live steam temperature (T.sub.steam) is controlled
by adjusting the inlet temperature in the inlet temperature
affecting air inlet system (12c).
14. Method according to claim 1, characterized in that the live
steam temperature (T.sub.steam) is determined as function of a
temperature of a steam turbine rotor and/or a steam turbine stator
part.
15. Combined cycle power plant comprising, a gas turbine (11) with
an inlet temperature affecting air inlet system (12a-c) for
adjusting the temperature of inlet air, a compressor (14)
downstream of the inlet temperature affecting air inlet system
(12a-c), for increasing the pressure of the air, and which is
equipped with variable inlet guide vanes (13) for adjusting the
inlet mass flow, at least one combustor (15, 15') downstream of the
compressor for combustion fuel with compressed air from the
compressor, at least one turbine (16, 16') downstream of the
combustor for expanding hot combustion gases thereby generating
mechanical power; a HRSG (18) downstream of the gas turbine (11)
for generating live steam; a steam turbine (18) for expanding the
live steam thereby generating mechanical power; and a control
system (22) characterized in that, the control system (22)
comprises a closed loop control scheme, which is configured to
generate a control variable indicative of the live steam
temperature (T.sub.steam1), and to control the inlet temperature
affecting air inlet system (12a-c) and/or the variable inlet guide
vanes (13) in accordance with said control variable such that
during operation of the combined cycle power plant the live steam
temperature (T.sub.steam) is kept at or above a desired target
steam temperature (T.sub.steam,t).
Description
TECHNICAL FIELD
[0001] The present invention relates to the technology of combined
cycle power plants. It refers to a method for operating a combined
cycle power plant with an inlet temperature affecting air inlet
system with variable inlet guide vanes for adjusting the inlet mass
flow. It further refers to a combined cycle power plant for being
used with such a method.
PRIOR ART
[0002] At part load the turbine outlet or exhaust gas temperature
(TAT) of a gas turbine strongly decreases (see for example document
EP 0 718 470 A2). A water/steam cycle coupled to the gas turbine in
a combined cycle fashion (via a HRSG) cannot be operated
effectively at a low temperature. Especially the lifetime
consumption of the respective steam turbine caused by a transient
cooling-down is high.
DESCRIPTION
[0003] For gas turbines with sequential combustion, a special Low
Load Operation Concept (LLOC) offers the possibility to keep the
entire combined cycle plant running and connected to the power grid
at very low load (<25%) in emission compliance with the first
combustor of the gas turbine operating in lean operation, during
times of low power demand/power tariffs instead of shutting it
down, with all the advantages related.
[0004] The Low Load Operation Concept [0005] avoids frequent power
plant start-stop-cycles at times during low grid demands, e.g.
during the night or weekend. Avoiding start-stop cycles leads to
reduced stress accumulation and lifetime consumption of major plant
equipment, even for equipment which has no lifetime counter
installed (heat recovery steam generator HRSG, piping, etc.); and
[0006] keeps the plant running at very low loads, allowing for very
quick response to sudden power demand or increasing spark spreads
(gross margin between electricity and fuel price).
[0007] The Low Load Operation Concept makes use of the shut down of
the sequential (second) combustor at low part loads while firing
the first combustor higher. The low load operation concept
parameters are determined by GT operation parameters like
compressor variable inlet guide vane (VIGV) setting and the firing
temperature.
[0008] However, the known LLOCs can still result in a reduced
exhaust temperatures, and typically still have some disadvantages:
[0009] High preparation time for low load operation, limiting the
operational flexibility, due to the fact that the steam turbine
(ST) has to be cooled down gradually to a sufficient low
temperature; [0010] impact on the Equivalent Operating Hours (EOH)
of the steam turbine due to a steam temperature reduction; and
[0011] loading speed to base load limited by steam turbine
stress.
[0012] The following specifications should eliminate these
drawbacks: [0013] No preparation time: the operator can activate
the LLOC mode at any time required; [0014] no EOH impact for the
steam turbine, due to a lower steam temperature reduction; [0015]
fast loading/de-loading.
[0016] The use of compressor outlet gas recirculation as well as
the use of an air conditioning system to control the inlet
temperature of a gas turbine for anti icing operation is known for
example from EP 2 180 165 A2.
[0017] Another document (JP4684968 B2) discloses a high moisture
gas turbine plant, which is excellent in output and efficiency in
non-rated load operation, and a respective control method. The high
moisture gas turbine plant comprises a turbine, a compressor, a
humidifying tower for humidifying compressed air, a regenerative
heat exchanger for heating the humidified air by exhaust gas, a
combustor operating with the heated air and fuel so as to generate
combustion gas, a compressor inlet guide vane controlling a flow
rate of combustion air, a compressor outlet pressure detector, an
exhaust temperature detector, a water supply amount detector
detecting the supply amount to the humidifying tower; and a control
device calculating a set value of an exhaust temperature from
output pressure detected by the compressor outlet pressure detector
and the water supply amount detected by the water supply amount
detector, so that opening of the compressor inlet guide vane is
adjusted to make the exhaust temperature be close to the calculated
set value, by using a function defining the set value of the
exhaust temperature in partial load operation by the outlet
pressure of the compressor.
SUMMARY OF THE INVENTION
[0018] It is an object of the present disclosure to provide a
method for operating a combined cycle power plant CCPP.
[0019] It is another object of the disclosure to provide a CCPP for
being used with the method according to the invention.
[0020] One aspect of the present disclosure is to propose a method
for operation of a combined cycle power plant, which allows
operation at low part load. The method is proposed for a combined
cycle power plant comprising, a gas turbine with an inlet
temperature affecting air inlet system for adjusting the
temperature of inlet air, a compressor downstream of the inlet
temperature-affecting air inlet system, for increasing the pressure
of the air, and which is equipped with variable inlet guide vanes
for adjusting the inlet mass flow, at least one combustor
downstream of the compressor for combustion of fuel with compressed
air from the compressor, and at least one turbine downstream of the
combustor for expanding hot combustion gases thereby generating
mechanical power. The combined cycle power plant further comprises
a HRSG downstream of the gas turbine for generating live steam, a
steam turbine for expanding the live steam thereby generating
mechanical power, and a control system. According to the proposed
method, a control variable indicative of the live steam temperature
is generated in a closed loop control scheme, and the inlet
temperature affecting air inlet system and/or the variable inlet
guide vanes are controlled in accordance with said control variable
such that the live steam temperature is kept at or above a desired
target steam temperature.
[0021] According to an embodiment of the disclosed method the live
steam temperature is directly measured and the measured temperature
is used as the control variable.
[0022] According to another embodiment of the method the turbine
outlet temperature is used as variable indicative of the live steam
temperature, and the turbine outlet temperature is used as the
control variable.
[0023] According to one further embodiment of this method the
turbine outlet temperature is directly measured.
[0024] According to another embodiment of the method the turbine
outlet temperature is calculated from an on-line heat balance
calculation and used as variable indicative of the live steam
temperature.
[0025] According to another embodiment of the method emissions,
especially NOx, at the outlet of the gas turbine is measured and
used as the control variable.
[0026] According to just another embodiment of the method a
temperature is measured at other parts of the gas turbine,
especially at the last stage vanes of the turbine, and this
measured temperature is used as a control variable.
[0027] According to a further embodiment of the method the inlet
air is heated in the inlet temperature affecting air inlet system
until live steam temperature is at or above the target steam
temperature. In order to carry out this method the air inlet
temperature affecting air inlet system is designed to heat up the
inlet air.
[0028] Especially, compressed air from a rear stage of the
compressor is used to heat up the inlet air in the air inlet
temperature-affecting air inlet system. A rear stage is any stage
downstream of the first compressor stage. Often the stages of the
second half of the compressor are referred to as rear stages. More
specifically the last two or three stages of a compressor can be
referred to as rear stage.
[0029] According to another embodiment of the method part of the
flue gases are recirculated and admixed to the inlet air in the
inlet temperature affecting air inlet system to heat up the inlet
air. For flue gas recirculation the combined cycle power plant
typically also comprises a flue gas splitter arranged downstream of
the HRSG dividing the flue gases into a flue gas flow for disposal
to the environment or further treatment and into one flue gas flow
for recirculation, a control device to control the recirculated
flue gas mass flow, and a re-cooler to control the temperature of
the recirculated flue gas before it is mixed with fresh ambient air
in the air inlet temperature-affecting air inlet system.
[0030] In yet another embodiment of the method a cooling air mass
flow of the gas turbine is reduced to increase turbine outlet
temperature and thus the live steam temperature. Alternatively or
in combination a re-cooling temperature of a cooling air cooler is
increased to increase the live steam temperature.
[0031] According to another embodiment of the method the inlet
temperature-affecting inlet system is designed to cool down the
inlet air. Cooling down the inlet temperature can extend the
operationability at high ambient temperatures. Further, depending
on the design and operating conditions the loading of a cold or
warm combined cycle power plant has to be stopped at so called hold
points where the gas turbine is operated for a certain time until
critical components of the turbine reach threshold temperature
values. After these threshold values are reached the gas turbine
can be further loaded. By cooling the inlet temperature the gas
turbine power at a threshold value can be increased. Due to the
resulting lower steam temperature with inlet cooling it might even
be possible to continue loading without delay at a threshold value.
After reaching the target load or base load the steam turbine
gradually heats up and a reduction in inlet cooling over time is
possible until eventually the inlet cooling can be completely
switched off.
[0032] According to a further embodiment of the method the inlet
temperature affecting air inlet system comprises an air
conditioning system for the inlet air.
[0033] According to another embodiment of the method water is
injected in the inlet temperature affecting air inlet system. For
this method the inlet temperature-affecting inlet system comprises
a water injection system.
[0034] According to still another embodiment of the method the gas
turbine is operated with sequential combustion and comprises two
combustors and two turbines. In particular during operation when
the inlet air temperature is increased in the inlet
temperature-affecting inlet system the second combustor is not
operating.
[0035] Besides the method a combined cycle power plant, which is
designed to carry out such a method, is an object of the
disclosure.
[0036] The disclosed combined cycle power plant comprises a gas
turbine with an inlet temperature affecting air inlet system for
adjusting the temperature of inlet air, a compressor downstream of
the inlet temperature-affecting air inlet system, for increasing
the pressure of the air, and which is equipped with variable inlet
guide vanes for adjusting the inlet mass flow, at least one
combustor downstream of the compressor for combustion of fuel with
compressed air from the compressor, and at least one turbine
downstream of the combustor for expanding hot combustion gases
thereby generating mechanical power. It further comprises a HRSG
downstream of the gas turbine for generating live steam, a steam
turbine for expanding the live steam thereby generating mechanical
power, and a control system. The control system is characterized in
that, it comprises a closed loop control scheme, which is
configured to generate a control variable indicative of the live
steam temperature, and to control the inlet temperature affecting
air inlet system and/or the variable inlet guide vanes in
accordance with said control variable such that during operation of
the combined cycle power plant the live steam temperature is kept
at or above a desired target steam temperature. To keep the live
steam temperature at or above the target steam temperature the VIGV
is closed, wherein the closure of the VIGV is a function of the
deviation to the target temperature. Further, to increase the steam
temperature the inlet temperature can be raised and to decrease the
steam temperature the inlet temperature can be reduced by inlet
temperature-affecting air inlet system.
[0037] The controller of the plant has a first output connected to
said inlet temperature affecting air inlet system, and a second
output connected to said variable inlet guide vanes.
[0038] According to an embodiment of the disclosed gas turbine said
control variable generating means comprises a temperature sensor,
especially for direct measurement of the turbine outlet
temperature.
[0039] According to another embodiment of the disclosed gas turbine
the temperature-affecting air inlet system is designed to heat up
the inlet air. Especially, compressed air from a rear stage of the
compressor is fed back into the inlet temperature affecting air
inlet system via a control valve, which is connected to the
controller.
[0040] According to another embodiment of the disclosed gas turbine
the inlet temperature affecting air inlet system is designed to
cool down the inlet air. According to a further embodiment of the
disclosed gas turbine the inlet temperature affecting air inlet
system is designed to inject water into the stream of inlet
air.
[0041] According to just another embodiment of the disclosed gas
turbine the inlet temperature affecting air inlet system comprises
an air conditioning system for the inlet air, which is connected to
the controller.
[0042] According to another embodiment of the disclosed gas turbine
the gas turbine is designed for sequential combustion and comprises
two combustors and two turbines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] Further characteristics and advantages will be more apparent
from the description of a preferred but non-exclusive embodiments
and with reference to the attached drawings.
[0044] FIG. 1 shows a schematic diagram of a combined cycle power
plant (CCPP) with a gas turbine according to an embodiment with a
controlled inlet temperature affecting air inlet system for heating
up the inlet air;
[0045] FIG. 2 shows, similar to FIG. 1, a schematic diagram of a
combined cycle power plant (CCPP) with a gas turbine according to
another embodiment with a controlled inlet temperature affecting
air inlet system for heating air-conditioning the inlet air;
[0046] FIG. 3 shows, similar to FIGS. 1 and 2, a schematic diagram
of a combined cycle power plant (CCPP) with a gas turbine according
to a further embodiment with a controlled inlet temperature
affecting air inlet system for injecting water into the inlet air
for fogging or high-fogging; and
[0047] FIG. 4 shows, similar to FIGS. 1 to 3, a schematic diagram
of a combined cycle power plant (CCPP) with a gas turbine according
to a further embodiment with a flue gas recirculation into the
inlet air for heating air-conditioning the inlet air; and
[0048] FIG. 5 shows an exemplary diagram for the control effect of
the disclosed method and gas turbine.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0049] According to the disclosure, a combined cycle power plant
has a closed loop control controller that adjusts the amount of air
inlet cooling or air inlet heating or that regulates the inlet
guide vane angle so that the live steam temperature or detected
turbine outlet temperature is kept to the desired setting
value.
[0050] In an embodiment, an exhaust gas temperature sensor in the
turbine exhaust diffuser senses the exhaust gas temperature. A gas
turbine inlet device (such as chiller, air pre-heater and/or
anti-icing system) and an inlet guide vane angle actuator are used
in a closed loop control scheme in order to keep the detected
exhaust gas temperature to a desired setting value. The disclosed
method can be used in a gas turbine plant, or in a combined cycle
power plant CCPP:
Advantage:
[0051] The exhaust gas temperature of the gas turbine can be
regulated to a desired value during gas turbine operation.
Consequently, the exhaust gas energy of the gas turbine can be
maintained to such a level that bottom cycles of the CCPP or a
cogeneration plant can continue to operate without excessive live
time consumption due to transient changes in the operating
conditions. Preferably it can continue to operate at design (or
close to design) conditions.
[0052] FIG. 1 shows a schematic diagram of a combined cycle power
plant (CCPP) 10a with a gas turbine 11 according to an embodiment
with a controlled inlet temperature affecting air inlet system 12a
for heating up the inlet air. The gas turbine 11 comprises the
inlet temperature affecting air inlet system 12a, which receives
air 12 at its inlet, a compressor 14 with variable inlet guide
vanes (VIGV) 13, a (first) combustor 15, a (first) turbine 16, and
a water/steam cycle 17 with a heat recovery steam generator (HRSG)
18, a steam turbine 19, a condenser 20, and a feedwater pump
21.
[0053] The exhaust gases of the turbine 16 pass the heat recovery
steam generator in order to generate the necessary steam for the
water/steam cycle 17. The temperature of the exhaust gas is--in
this embodiment--directly measured by means of a temperature sensor
30 at the exit of the turbine 16. Additionally the temperature of
the live steam is measured with a steam temperature sensor 38. The
measured TAT and/or the live steam temperature value are used as an
input variable for a control 22, which controls the operation of
the inlet temperature affecting air inlet system 12a and/or the
variable inlet guide vanes 13.
[0054] The inlet temperature affecting air inlet system 12a
receives hot compressed air extracted at a rear stage of the
compressor 14. This compressed hot air is fed into the inlet
temperature affecting air inlet system 12a via a shut-off valve 23,
a control valve 24, an orifice 25 and a silencer 26. The control
valve 24 is connected to a control output of the control 22.
[0055] As is shown in FIG. 1 (and FIGS. 2, 3, and 4) by dashed
lines, the gas turbine 11 may have a sequential combustion with a
second combustor 15' and a second turbine 16', which is then
followed by the water steam cycle.
[0056] FIG. 2 shows another embodiment, with a different inlet
temperature affecting air inlet system 12b, which comprises an air
conditioning system 27 for affecting the temperature of the inlet
air 12 before entering the compressor 14. In this case, the
variable inlet guide vanes 13 and the air conditioning system 27
are controlled by the controller 22. The heat required or released
by the air conditioning system 27 can be provided or used. For
example a heat source or a heat sink can be provided by the water
steam cycle of the plant. The released heat can for example be used
to preheat water. Low-grade heat can be used as a heat source.
[0057] FIG. 3 shows a further embodiment, with a different inlet
temperature affecting air inlet system 12c, which comprises means
for injecting water 28 into the inlet air. The amount of water
injected is controlled by means of a control valve 29 being
connected to a control output of controller 22. However, other
control means for the water injection are possible.
[0058] The water injection may happen by means of a fogging or high
fogging system, e.g. a system comprising high-pressure pumps and
atomizer nozzles.
[0059] Alternatively, the inlet temperature affecting air inlet
system may comprise a chilling system or an evaporative cooler
system.
[0060] FIG. 4 shows a further embodiment, with a different inlet
temperature affecting air inlet system 12d, which comprises means
for introducing recirculated flue gas 34 into the inlet air for
heating air-conditioning the inlet air. The recirculated flue gas
is branched of from the flue gas flow leaving the HRSG 18 in a flue
gas splitter 36. The mass flow of recirculated flue gas 34 is
adjusted by the damper or recirculation flow control valve 37. To
compensate for the pressure losses of the recirculation system a
blower or variable speed blower 33 may be arranged in the flue gas
ducting. In this example the recirculated flue gas can be re-cooled
in a flue gas re-cooler 33 to avoid large temperature
inhomogeneities in the inlet air.
[0061] Alternatively, the inlet temperature affecting air inlet
system may comprise an air pre-heater system with an external heat
source instead of re-circulating air from the compressor outlet to
the compressor inlet.
[0062] In general, a closed loop control uses the exhaust gas
temperature (TAT) as input to the control system and controls the
gas turbine operation with optimization of the exhaust gas
temperature.
[0063] The control is done by controlling at least one of the
following parameters: [0064] The position of the variable inlet
guide vanes VIGV; [0065] md the inlet bleeding mass flow by
regulating the position of a control valve 24; [0066] regulating
the position of a control valve 29, which regulates the mass flow
of air inlet cooling water 28; [0067] regulating the position of a
control valve, which regulates the fuel mass flow injected in a
combustor 15, 15' (not shown in FIG. 1-4).
[0068] Instead of measuring the TAT or live steam temperature
directly (with temperature sensor 30 or 38) the control system
input could also be a calculated TAT from an on-line heat balance
calculation.
[0069] Alternatively, if the direct TAT measurement is not
available or unusable, other indirect input variables could be
used: [0070] emissions at the gas turbine outlet (e.g. NOx), or
[0071] temperature measurements elsewhere (temperature sensor
inputs 31 in FIG. 1-4), e.g. on the last stage vane of the turbine,
which is normally un-cooled.
[0072] In addition to measuring the exhaust gas temperature TAT,
the compressor inlet and outlet temperatures may be measured.
[0073] Further parameters of interest relate to ambient conditions
(ambient temperature, ambient pressure, ambient humidity)
[0074] Other parameters are the inlet pressure drop, the water mass
flow sprayed by fogging and high fogging systems, the water mass
flow circulating in an evaporative cooler, the water/steam mass
flow injected in the combustor 15, 15'.
EXAMPLE
[0075] An air recirculation system according to FIG. 1 (also called
anti-icing) in operation during Low Load Operation has been
introduced for a power plant comprising gas turbines of the type
GT26. In order to reach a turbine exhaust temperature high enough
to keep the CCPP in operation during low load demands without
penalty (like steam turbine lifetime penalty), the anti-icing
system is switched on and operates in closed loop control.
[0076] FIG. 5 shows the expected turbine exhaust temperature TAT
and the air recirculation mass flow ARMF as a function of ambient
temperature Tamb during low load operation if the system is in
operation. When the ambient temperature Tamb falls below a certain
level (e.g. 22.degree. C.) the corresponding decrease in turbine
exhaust temperature TAT is stopped by starting and increasing the
air recirculation mass flow ARMF. The concept includes also a
regulation of VIGV position in order to optimize the exhaust
temperature.
[0077] In a CCPP the aim is a control of the live steam temperature
Tsteam. This temperature can be measured directly or controlled via
the TAT.
[0078] A target temperature Tsteam,t is set for a gas turbine load
and the steam temperature Tsteam is controlled by means of the
variable inlet guide vanes VIGV and conditioning of the compressor
inlet conditions.
[0079] The conditioning comprises at least one of: [0080] a control
of the inlet temperature; [0081] pre-heating by means of an
anti-icing system, i.e. the recirculation of compressor outlet air
or extracted air (see EP 2 180 165); [0082] pre-heating by
recirculation of exhaust gas (see US 2008/0309087); [0083]
pre-heating by means of another heat source, like steam form the
water/steam cycle, or the like; [0084] cooling; [0085] control of
the inlet gas composition; [0086] water injection or wetting
[0087] At low partial load the cooling air can be reduced, thereby
increasing the TAT and Tsteam.
[0088] Typically a control will be limited to a pre-heating for
most operating conditions. Cooling may be necessary for example
during loading of a cold plant or in certain extreme cases with
very high ambient temperature.
[0089] The target value of the live steam temperature Tsteam,t can
be a definite function of the load. However, Tsteam,t can also
depend on a rotor or stator temperature of the steam turbine. When
the rotor or stator is not yet warmed up completely, Tsteam,t may
be lower. With the warming-up of rotor and stator Tsteam,t changes
with time.
[0090] In an embodiment, the gas turbine control keeps the gas
turbine at a minimum load, where the Tsteam,t can just be
maintained.
* * * * *